Carrier frequency communication exchange system



- in the art.

Patented Nov. 18, 1941 UNITED STAT alum na Wolfgang Hagen, Berlin,

FREQUENCY COMMUNICATION EXCHANGE SYSTEM- Germany, assignor to C.

. Lorenz Aktienge'sellschaft, Berlin-Tempelhof,

' Germany, a company Application June 28; 1939, Serial No. 281,520

In Germany July 21, 1938 2Claims'. (01. 179-45) The present invention relates to carrier frequency communication exchange systems, andv more particularly to telephone exchanges in which carrier frequency message currents are impressed upon telephone subscriber lines'interconnected therewith.

In cases that the subscriber lines of a telephone exchange system, in addition to their ordinary task, are likewise adapted to transfer carrier frequency message currents to their respective subscribers substations, electric filter devices must be provided in such exchange in order to enable the carrier currents to be satisfactorily applied to these lines and to suppress-interferences caused by spurious currents occasioned in the equipment of the telephone exchange. It is a natural requirement to make these filters as compact as ever possible, by bearing in mind that a very large number thereof must be disposed in the exchange since each outgoing line adapted to transmit carrier messages must be provided with such filter.

The electric filter devices used in exchange systems of the above mentioned type generally comprise a low-pass filter which has for its object to suppress harmful oscillations caused by the circuit elements of the exchange system, such as the selector switches, for example. Moreover, means such as coupling condensers must also be present for impressing the carrier frequency currents upon the telephone lines.

My invention consists in certain features of novelty which will clearly appear from the following description and be pointed out in the appended claims, reference being had to the accompanying drawing, in which Fig. l diagrammatically shows a conventional filter arrangement known in the art, while Fig. 2 is a diagrammatic showing of a corresponding filter device according to this invention and its improvements over that shown in the Fig. 1.

First referring to Fig. 1, there is shown a filter device of the above mentioned type per se known A low-pass filter indicated by the dash line rectangle W comprising two series inductance branches and two cross branches formed by condensers Cl and C2 is connected between the terminals 0. and b of an outgoing subscriber line and the terminals a and 12' connected with the exchange equipment, e. g. the selector switches thereof. Carrier frequency message currents incoming at the terminals and d are impressed upon the outgoing telephone line a b over a transformer U and coupling condensers C. These additional coupling condensers lOt substantially complicate the filter arrangement and, moreover, frequently encounter the hardly solvable problem of stowing in the customary very restricted space available in telephone exchange equipments.

According to one object of my invention, the heretofore mentioned difficulties are overcome by so designing a telephone exchange filter .device, that the cross branch condensers-per se required in th'elow-pass filter thereof for protecting the subscribers lines against spurious oscillations from the circuit elements of the exchange equipment are concurrently utilized as coupling condensers for impressing the carrier frequency message currents upon such lines, so that additional coupling condensers for the last mentioned purpose may be omitted.

According to a further object of this invention, the cross branch condensers of a low-pass filter are simultaneously used for suppressing the cophasal interference oscillations occurring at the low frequency end of such filter when employed in a manner and for the purpose mentioned above.

The Fig. 2 is illustrative for the new arrangement according to my invention. In this figure,

the outgoing subscribers line is denoted a, b, the

terminals, interconnecting the filter W with the exchange equipment, are shown at a and b, and the carrier frequency source is indicated at c and d in the same manner as shown in Fig. 1. In the novel circuit arrangement according to my invention, the condenser Cl shown in Fig. l as a member of symmetrical structure 'of the filter W is subdivided into two partial condensers Ca which are connected in series with one another through the intermediate secondary winding of the transformer U between the two series branches L of the filter. The carrier frequency message currents incoming at c and d are thus impressed upon the outgoing subscriber line a, I) through the transformer U and over the condensers Ca. This facility involves the essential advantage that the filter device becomes substantially simplified.

Also the cross branch condenser C2 shown in Fig. 1 has been subdivided into two partial condensers Cb as embodied in Fig. 2. These two condensers are connected in series with one another across the two series branches L of the filter and the mid-point between these two condensers is grounded as indicated at E. It is thus possible to fully suppress the cophasal spurious oscillations occurring on the exchange equipment side a, b of the filter since these oscillations are leaked off to ground through the condensers Cb. The inductance coils L of Fig. 2 are the same as the coils L shown in Fig. 1.

The novel improvement in electric filter devices above disclosed involves the beneficial features that not only the condensers heretofore employed in filter devices of the type referred to above may simultaneously and concurrently'be used as the coupling condensers for impressing carrier frequency message currents upon the outgoing subscriber lines, but also that interference oscillations set up in certain circuit elements of the exchange equipment may be satisfactorily leaked ofi to the earth through the series condensers shunted across the terminals through which the filter is connected with the exchange equipment.

My invention is by no means restricted to circuit arrangements as set forth in this specification and illustrated in the drawing by way of example, but is likewise applicable to all asymmetric filter devices and complicated Wave filter networks.

What is claimed is:

1. In a telephone exchange system which comprises exchange equipment for establishing ordinary telephonic conversation connections, outgoing bifilar subscriber lines, a low-pass filter connected between each of said subscriber lines and said exchange equipment, each of said filters comprising two inductance coils, each forming a series branch, a first condenser assembly shunted across the ends of said series branches connected to said exchange equipment, and a second condenser assembly shunted across the ends of said series branches connected to said subscriber lines, said second condenser assembly being an electrical component of the low-pass filter and comprising two substantially equal series capacities, the effective across-the-line shunt capacitance of said two series capacities taken together, being of approximately the same magnitude as the across-the-line shunt capacitance of a single capacitor which would conventionally be employed as the terminating branch of the low-pass filter, a source of carrier frequency currents, and means for connecting said source between said two substantially equal series capacities and in series therewith whereby said carrier frequency currents are impressed upon a predetermined one of said outgoing subscriber lines.

2. A system according to claim 1, wherein the said first condenser assembly comprises two capacities in series with one another having their junction point connected to ground for leaking off thereto spurious oscillations set up in the said exchange equipment.

WOLFGANG HAGEN. 

